Integrated circuits in many instances comprise a large number of transistors. The memory cell array of an integrated semiconductor memory, for example, of a DRAM (=Dynamic Random Access Memory) semiconductor memory, comprises a multiplicity of memory cells constructed from in each case a selection transistor and a storage capacitor. The memory cells are arranged in matrix form between word and bit lines. A control terminal of a respective selection transistor of a DRAM memory cell is connected to one of the word lines. For a read or write access to the DRAM memory cell, the selection transistor is turned on by being driven with a corresponding control signal on the word line, so that the storage capacitor is connected to the connected bit line via the turned-on path of the selection transistor. In the event of a read access, the charge stored on the electrodes of the storage capacitor results in a change in potential on the connected bit line via the turned on path of the selection transistor. In the event of a write access, an item of information is stored in the memory cell via the turned on path of the selection transistor by the electrodes of the storage capacitor being charged to a high or low voltage level. The behavior of the selection transistors is therefore of crucial importance both for read operations and for write operations of the integrated semiconductor memory.
The behavior of the transistors can be determined most simply based on a family of characteristic curves, for example, an IDS/UDS family of characteristic curves or an IDS/UG family of characteristic curves. Such families of characteristic curves of transistors within an integrated circuit can only be determined at the wafer level at the present time. In the case of an integrated semiconductor memory, for example, special test structures of transistors are arranged within the sawing frame, the so-called scribe line. The gate, source, and drain terminals of the transistors can be contact-connected to probes of a test system via specially provided terminal pads. By driving the gate, source and drain terminals with control voltages generated by the test system, it is possible to determine families of characteristic curves of the test transistors. When the individual semiconductor chips are sawn out of the wafer, the test structures are lost, however. Therefore, there is no longer a possibility of recording families of characteristic curves of transistors of an integrated circuit which are already situated in a finished housed device.
It is found in an integrated circuit that many circuit components, in particular, transistors, fail even after a short operating duration. It is of particular interest, therefore, to record and compare families of characteristic curves of transistors at the beginning of their life cycle and after a certain operating duration in order to be able to make a reliable statement about the failure probability of the transistors. However, since a shortest possible test phase of integrated circuits is of interest, the circuit components are artificially aged in the context of a burn-in test. For this purpose, the circuit components of the integrated circuit are exposed to a higher operating voltage and an increased temperature for the duration of the burn-in test. Depending on the magnitude of the voltage with which the devices are operated and the temperature to which the circuit components are exposed, operating times longer than the actual length of the test can thus be artificially generated. In order to be able to make a statement about the failure probability of a transistor, it is desirable to record and compare the family of characteristic curves of a transistor before and after the conclusion of a burn-in test. However, since the burn-in test is carried out on the finished housed device, at the present time, it is not yet possible to determine families of characteristic curves of transistors in the context of a burn-in test.
An integrated circuit which can be used to determine families of characteristic curves of circuit components of an integrated circuit, in particular, of transistors, at the component level and a method which makes it possible to determine families of characteristic curves of circuit components of an integrated circuit, in particular, current/voltage characteristic curves of transistors are desirable.